Project Summary Type 1 diabetes (T1D) is an autoimmune disease that destroys the pancreatic ? cells that produce insulin. Over 30,000 Americans, mostly children and adolescents, will develop T1D this year. Many will go on to suffer blindness, kidney failure, and stroke as a result of their diabetes. While we can identify individuals at risk for the disease, currently there are no approved treatments that prevent T1D. We recently identified a novel target molecule that contributes to the development of T1D. Hyaluronan (HA) is an extracellular matrix (ECM) polymer that is abundant in islets under autoimmune attack. HA polarizes local immune responses towards a pro-inflammatory Th1 T-cell phenotype and prevents induction of pro- tolerogenic, Foxp3+ regulatory T-cells (Treg), thereby contributing to the pathogenesis of T1D. We have also identified a compound that may prevent T1D. 4-methylumbelliferone (4-MU) is an oral inhibitor of HA synthesis, which clears islet HA deposits and prevents diabetes in multiple animal models of T1D, including in DORmO and Non Obese Diabetic (NOD) mice. These effects are associated with an increase in pro-tolerogenic, Foxp3+ Tregs and prevention of ? cell destruction. Our data suggest that it may be possible to prevent T1D in humans by targeting HA synthesis with 4-MU, our lead compound. These results are particularly exciting because 4-MU is already an approved drug. Called ?hymecromone?, it has been prescribed for >40 years to treat biliary spasm. It is safe, well-tolerated, approved in children as well as adults, and could be an ideal oral agent to prevent progression to T1D. Unfortunately, 4-MU has poor pharmacokinetics that precludes its clinical use for T1D prevention. In particular, oral 4-MU has low bioavailability. Consequently, large doses of 4-MU are required in our animal models. Administration of comparable regimens is impractical in humans, such that it is not possible to repurpose 4-MU for human T1D prevention. We need an improved version of 4-MU with better bioavailability. A pro-drug strategy is often used to improve the bioavailability of phenolic compounds like 4-MU, our prototype lead compound. In proof of principle studies we have generated a 4-MU pro-drug which delays the onset of autoimmune diabetes, demonstrating that this approach is feasible and pharmacologically sound. Along with these efforts to improve upon the bioavailability of 4-MU, we also need to understand what tissue levels of 4-MU are required to effectively target islet HA synthesis. Further, we need to define the relationship between oral 4-MU dosage and islet 4-MU exposure. Here, we propose a systematic framework for the pharmacologic evaluation of 4-MU, for the generation of 4-MU pro-drugs, and for their functional assessment in well-validated and predictive animal models of autoimmune diabetes. Together, these early-stage, pre-clinical studies will establish the mechanistic and pharmacologic foundations necessary to for ADME studies in humans and a human phase I clinical trial.